Abstract A critical need exists for highly sensitive and specific serodiagnostic tests to discriminate infections by pathogenic arboviruses in geographic regions, such as Brazil, where multiple flaviviruses including Zika virus (ZIKV), four serotypes of dengue virus (DENV1-4), West Nile virus (WNV), and yellow fever (YFV), as well as chikungunya virus (CHIKV), Mayaro virus (MAYV) (both alphaviruses) and Oropouche virus (OROV) (a bunyavirus), are endemic. However, cross-reactivity of antibodies against different flaviviruses present major challenges, such that even neutralization tests cannot confirm a specific flavivirus infection among individuals who have experienced previous flavivirus infections. The objective of the proposed research is to develop highly sensitive and specific serodiagnostic tests to discriminate infections by pathogenic arboviruses. The central hypothesis is that a combination of fusion loop (FL)-mutated VLPs and nonstructural protein 1 (NS1) proteins of different flaviviruses and recombinant proteins and VLPs of CHIKV, MAYV and OROV in multiplex formats can distinguish different arbovirus infections. The first Aim is to develop and validate multiplex IgG and IgM microsphere immunoassays (MIAs) based on recombinant proteins to distinguish arbovirus infections. We will employ recombinant NS1 proteins of 7 flaviviruses, envelope (E) 2 protein and nucleocapsid (N) protein of CHIKV, MAYV and OROV for multiplex IgG and IgM MIAs using Luminex 200 and test with 15 panels of convalescent-phase serum/plasma from individuals with confirmed arbovirus infections. The second Aim is to develop and validate multiplex IgG and IgM MIAs based on VLPs to distinguish arbovirus infections. We will use purified and FL-mutated VLPs of 7 flaviviruses and VLPs of CHIKV, MAYV and OROV, and test with 15 panels of serum/plasma as in Aim 1. The third Aim is to compare the multiplex IgM MIAs and IgG MIAs with currently available serodiagnostic assays to determine arbovirus seroprevalence in Bahia, a northeastern state with multiple arbovirus transmissions in Brazil. For serodiagnosis, we will test serum samples from patients with acute febrile illness and their follow-up at outpatient clinics of 4 study sites (Salvador, Feira de Santana, Itabuna and Campo Formoso) in Bahia. For seroprevalence study, we will enroll and test household members at communities of the 4 study sites. The proposed study is innovative as it employs two promising antigens (NS1 protein and FL-mutated VLPs) to overcome flavivirus cross-reactivity for seven flaviviruses, as opposed to traditional E protein-based tests, plus CHIKV, MAYV and OROV in two multiplex formats to discriminate arbovirus infections in Brazil. It would contribute to a detailed understanding of the epidemiology of 10 arbovirus infections in Bahia. The successful employment of the multiplex platforms can serve as a new paradigm for serodiagnosis and serosurveillance in countries where multiple arboviruses co-circulate. Most importantly, this research will facilitate the implementation of arbovirus vaccines, in particular ZIKV, DENV and CHIKV vaccines in endemic regions.